Return-Path: Received: from [24.93.47.40] (HELO ms-smtp-01-eri0.texas.rr.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 3051625 for flyrotary@lancaironline.net; Sun, 29 Feb 2004 21:00:02 -0500 Received: from dell (cs6669241-190.austin.rr.com [66.69.241.190]) by ms-smtp-01-eri0.texas.rr.com (8.12.10/8.12.7) with SMTP id i211xpLe019219 for ; Sun, 29 Feb 2004 20:00:00 -0600 (CST) Message-ID: <008901c3ff30$dc893b00$6501a8c0@austin.rr.com> From: "Bob Darrah" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: PROP Free Spinning or WindMilling??? Date: Sun, 29 Feb 2004 19:59:41 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0086_01C3FEFE.9180EE00" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0086_01C3FEFE.9180EE00 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Jim Sower wrote (snip) >uite often stalled, so it produces more drag and less lift). At = cruise >airspeed, the forward velocity of the airplane becomes a = component of the >AoA and effectively reduces it making for smaller Cl = and Cd, but the >"airspeed" of the airfoil now has the airspeed of the = airplane added to >rotational speed, so this higher speed increases = total drag >(geometrically). High Cd at no airspeed and lower Cd at = higher airspeed >tend to wash out and we end up with cruise RPM not too = far removed from >static RPM.=20 >Power off: Let's assume a given airspeed (say 80 kias) on our fixed = pitch >prop.=20 > Engine "seized": Our prop is at whatever AoA is determined by = >measuring the wind velocity vector and the chord of the airfoil. It = will be >very high - basically 90' less the local pitch of the prop. = The=20 >drag will correspond to the airfoil drag at ?? AoA (say 50'-80') = depending >on where you measure along the span.=20 > Prop "freewheeling": (more snip). If our prop is 80% efficient = (is that >typical?), and our airplane requires 2400 RPM to cruise at 80 = kias, I would >intuit that the terminal rpm of the frictionless = freewheeling prop would be >2400/0.8 or about 3000 RPM.=20 Hay, that's faster than the engine can turn it-me thinks that if this = is true, we are getting something for nothing. But I do agree, a C-123 = prop in near FLAT pitch produces a whole lot of drag. Bob Darrah ------=_NextPart_000_0086_01C3FEFE.9180EE00 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Jim Sower wrote (snip)

>uite often stalled, so it produces more drag and less=20 lift). At cruise >airspeed, the forward velocity of the = airplane=20 becomes a component of the >AoA and effectively reduces it making = for=20 smaller Cl and Cd, but the >"airspeed" of the airfoil now has the = airspeed=20 of the airplane added to >rotational speed, so this higher speed = increases=20 total drag >(geometrically). High Cd at no airspeed and lower = Cd at=20 higher airspeed >tend to wash out and we end up with cruise RPM not = too far=20 removed from >static RPM.=20
>Power off: Let's assume a given airspeed (say 80 = kias) on=20 our fixed pitch >prop.
> Engine=20 "seized": Our prop is at whatever AoA is determined by = >measuring=20 the wind velocity vector and the chord of the airfoil. It will = be=20 >very high - basically 90' less the local pitch of the prop. = The=20
>drag will correspond to the airfoil drag at ?? AoA (say = 50'-80')=20 depending >on where you measure along the=20 span.

> Prop "freewheeling": = (more=20 snip). If our prop is 80% efficient (is that >typical?), and = our=20 airplane requires 2400 RPM to cruise at 80 kias, I would >intuit = that the=20 terminal rpm of the frictionless freewheeling prop would be=20 >2400/0.8 or about 3000 RPM.=20
Hay, that's faster than the engine can turn it-me thinks that if = this is=20 true, we are getting something for nothing. But I do agree, a = C-123 prop=20 in near FLAT pitch produces a whole lot of drag.

Bob Darrah

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